Off gas pedal gears 1-3 rpm's drop
 

I have a 2002 7.3 F250, no mods. 180000 mile. I noticed while coming home today in stop and go traffic. I will be going in first gear about 15 to 20 miles an hour let off the gas pedal RPMs drop to 750 then I have into second gear going approximately 30 mph or 35 mph The same thing I let off the RPMs drop to 750 the same thing happens in third gear but when I get fourth gear overdrive and I get up to 60 miles an hour plus I let off the gas and it holds my rpm's and slowly decreases do I have an issue with my torque converter or something else? This started about two weeks ago after pulling my trailer and found out icp. Bad ..........Fluid good